Carrier Transport and Electrical Conduction in Alloy-Mediated Graphene on Silicon
- Publication Type:
- Thesis
- Issue Date:
- 2020
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The possibility of graphene-based micro- and nanoelectronic devices that exploit the extraordinary electronic properties of graphene is the biggest inspiration behind the accelerated development of graphene science and technology. Although the remarkable efforts for establishing graphene as a new electronic material began over 15 years ago, the actual realisation of graphene devices on a large-scale remains elusive, mainly due to feasibility, cost-effectiveness and compatibility issues with the existing semiconductor technology and processes. Significant advancements have been achieved in the synthesis and establishment of transport properties of epitaxial graphene (EG) on 4H- and 6H-SiC, while equivalent progress using silicon (Si) as a platform (via a thin film of 3C-SiC) with reliable electrical transport measurements has not been elucidated to date, due to limitations such as non-uniform coverage of graphene on 3C-SiC/Si and high density of defects within the 3C-SiC.
In this work, we first show that the heteroepitaxial 3C-SiC on Si as the substrate should be carefully approached, as the 3C-SiC/Si heterojunction is electrically unstable and prone to severe leakage or parallel conduction. Subsequently, we find that the interface instability is due to the diffusion of carbon into the silicon matrix during the 3C-SiC growth, creating electrically active interstitial carbon. We overcome these challenges using 3C-SiC on a highly-resistive silicon substrate.
By addressing the parallel conduction issue of the 3C-SiC/Si heteroepitaxial system, in this work, we isolate the charge transport properties of epitaxial graphene (EG) grown directly on 3C-SiC over large areas via an alloy-mediated method and present corresponding physical ab-initio models. Here, we study the properties of EG synthesised on 3C-SiC(100) and 3C-SiC(111). The transport properties of EG on 3C-SiC follow a similar power-law dependence of sheet carrier concentration and mobility and comparable sheet resistance values with the EG on bulk-SiC – although the grain sizes for both are vastly different. Furthermore, we find that the transport properties of graphene within the observed regime are dominated by the substrate interaction, resulting in a large p-type doping, especially for the graphene on 3C-SiC(100). In the case of EG on 3C-SiC(111), the presence of buffer layer reduces the substrate interaction and the charge transfer up to an extent. This work demonstrates a more compelling need to focus on the engineering of the graphene-substrate interface as opposed to graphene grain sizes in order to tune the charge transport properties of the epitaxial graphene for the integration of 2D materials in functional nanosystems.
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